Additional Inherited Members

Detailed Description

The QTabletEvent class contains parameters that describe a Tablet event.

Tablet events are generated from tablet peripherals such as Wacom tablets and various other brands, and electromagnetic stylus devices included with some types of tablet computers. (It is not the same as QTouchEvent which a touchscreen generates, even when a passive stylus is used on a touchscreen.)

Tablet events are similar to mouse events; for example, the x(), y(), pos(), globalX(), globalY(), and globalPos() accessors provide the cursor position, and you can see which buttons() are pressed (pressing the stylus tip against the tablet surface is equivalent to a left mouse button). But tablet events also pass through some extra information that the tablet device driver provides; for example, you might want to do subpixel rendering with higher resolution coordinates (hiResGlobalX() and hiResGlobalY()), adjust color brightness based on the pressure() of the tool against the tablet surface, use different brushes depending on the type of tool in use (device()), modulate the brush shape in some way according to the X-axis and Y-axis tilt of the tool with respect to the tablet surface (xTilt() and yTilt()), and use a virtual eraser instead of a brush if the user switches to the other end of a double-ended stylus (pointerType()).

Every event contains an accept flag that indicates whether the receiver wants the event. You should call QTabletEvent::accept() if you handle the tablet event; otherwise it will be sent to the parent widget. The exception are TabletEnterProximity and TabletLeaveProximity events: these are only sent to QApplication and do not check whether or not they are accepted.

The QWidget::setEnabled() function can be used to enable or disable mouse, tablet and keyboard events for a widget.

The event handler QWidget::tabletEvent() receives TabletPress, TabletRelease and TabletMove events. Qt will first send a tablet event, then if it is not accepted by any widget, it will send a mouse event. This allows users of applications that are not designed for tablets to use a tablet like a mouse. However high-resolution drawing applications should handle the tablet events, because they can occur at a higher frequency, which is a benefit for smooth and accurate drawing. If the tablet events are rejected, the synthetic mouse events may be compressed for efficiency.

New in Qt 5.4: QTabletEvent includes all information available from the device, including QTabletEvent::buttons(). Previously it was not possible to accept all tablet events and also know which stylus buttons were pressed.

Note that pressing the stylus button while the stylus hovers over the tablet will generate a button press on some types of tablets, while on other types it will be necessary to press the stylus against the tablet surface in order to register the simultaneous stylus button press.

Notes for X11 Users

If the tablet is configured in xorg.conf to use the Wacom driver, there will be separate XInput "devices" for the stylus, eraser, and (optionally) cursor and touchpad. Qt recognizes these by their names. Otherwise, if the tablet is configured to use the evdev driver, there will be only one device and applications may not be able to distinguish the stylus from the eraser.

Notes for Windows Users

Tablet support currently requires the WACOM windows driver providing the DLL wintab32.dll to be installed. It is contained in older packages, for example pentablet_5.3.5-3.exe.

Returns the button state when the event was generated. The button state is a combination of buttons from the Qt::MouseButton enum using the OR operator. For TabletMove events, this is all buttons that are pressed down. For TabletPress events this includes the button that caused the event. For TabletRelease events this excludes the button that caused the event.

Returns the global position of the device at the time of the event. This is important on asynchronous windows systems like X11; whenever you move your widgets around in response to mouse events, globalPos() can differ significantly from the current position QCursor::pos().

Returns the global position of the device at the time of the event. This is important on asynchronous windows systems like X11; whenever you move your widgets around in response to mouse events, globalPosF() can differ significantly from the current position QCursor::pos().

Returns the tangential pressure for the device. This is typically given by a finger wheel on an airbrush tool. The range is from -1.0 to 1.0. 0.0 indicates a neutral position. Current airbrushes can only move in the positive direction from the neutrual position. If the device does not support tangential pressure, this value is always 0.0.

Returns a unique ID for the current device, making it possible to differentiate between multiple devices being used at the same time on the tablet.

Support of this feature is dependent on the tablet.

Values for the same device may vary from OS to OS.

Later versions of the Wacom driver for Linux will now report the ID information. If you have a tablet that supports unique ID and are not getting the information on Linux, consider upgrading your driver.

As of Qt 4.2, the unique ID is the same regardless of the orientation of the pen. Earlier versions would report a different value when using the eraser-end versus the pen-end of the stylus on some OS's.

int QTabletEvent::x() const

int QTabletEvent::xTilt() const

Returns the angle between the device (a pen, for example) and the perpendicular in the direction of the x axis. Positive values are towards the tablet's physical right. The angle is in the range -60 to +60 degrees.

int QTabletEvent::y() const

int QTabletEvent::yTilt() const

Returns the angle between the device (a pen, for example) and the perpendicular in the direction of the y axis. Positive values are towards the bottom of the tablet. The angle is within the range -60 to +60 degrees.